In recent years, increased emphasis has been placed on development of the internal combustion engine, particularly for vehicular applications, to produce engines having high power output per weight ratios, good fuel economy and maximum quality. Technological development has been rapid. A substantial portion of development work on the four-cycle internal combustion engine has been directed to increasing the power or total work of the engine by improving the combustion and expansion portion of the power cycle. To a lesser extent, development has centered around decreasing the amount of work expended during the intake and exhaust portions of the work cycle. In each case, attention has been directed to the intake and exhaust valve systems, their structure and control. Amongst these systems are those providing for variable valve timing for both the intake and exhaust valves, and for variable valve lift. The advantages of these mechanisms are numerous and fairly well known.
In many instances, the valves are operated by hydraulic control. This permits flexible control strategies, such as lost-motion valve lift systems wherein the pressurized fluid is drawn off in a controlled manner rather than being allowed to act directly upon the mechanisms controlling valve lift. Such a system has the advantage of providing for variable control of intake, timing, duration and valve lift. However, achieving a practical and cost-effective design using hydraulics can be difficult for several reasons. High system fluid pressure requires careful control of clearances between moving parts to limit fluid leakage. Similarly, sealing of assembled parts becomes difficult and usually requires elastomer seals. Yet another problem is the sealing of the porosity of aluminum castings which have many times been proposed for use in housing hydraulic components and high pressure auto passages to minimize weight.
An example of the more recently developed hydraulic valve control arrangements is shown in U.S. Pat. No. 4,671,221 wherein it is noted that the entire hydraulic mechanism includes: a cam follower, piston and pump actuated by the camshaft; an electromagnetic actuated valve for bleeding off the hydraulic fluid from the slave piston; an accumulator for storing the fluid temporarily bled from the system; and the hydraulically actuated slave piston which directly actuates the poppet valve (intake valve).
Similar systems are shown in U.S. Pat. No. 4,466,390 and U.S. Pat. No. 4,674,451.
In each case, the valve Control system, being located in a separate housing co-extensive with the cylinder head, or in the cylinder head itself, presents substantial manufacturing problems including the costs associated with manufacturing such an assembly, the sealing problems inherent in such a design, and the problem of assembling the system in a "clean" environment.
U.S. Pat. No. 3,963,006 is a further example of a hydraulically actuated valve train system, and in this case is built into the engine cylinder head as an integral part thereof.
Likewise, U.S. Pat. No. 1,760,853 shows a hydraulically actuated valve system designed as a single unit that may be adapted for ready attachment to the engine block and includes hydraulically actuated valve lift mechanisms for each of the intake and exhaust valves for the entire cylinder bank.
In light of these teachings, and considering the demands of the present automotive industry, the inventors felt there existed a need for developing a modular cartridge concept maximizing the usage of common hydraulic actuators among engine families, one which would permit hydraulic valve control to be more production feasible by improving the quality of design and reducing the cost, and one permitting the integration of the hydraulic components into subassemblies which could be assembled separately for the main engine assembly line in a "clean room" environment.
The present invention is directed towards these ends.